Both our statements are basically opinions, so I'll just explain mine in detail rather than just saying 'no, you're so wrong!'.
I understand that there are umpteen versions of the HK trigger system... of the ones I tried, none of them wowed me. If I was going to get a pistol with an external hammer like the USP, I'd probably go for traditional double / single. They're straightforward and shootable. If I were going to do that, though, I'd get a Sig instead, because their guns shoot so smoothly and the trigger feels right. I thought the trigger on my Bulgarian Makarov was at least as good as the trigger on some USP's I've shot, and the double action trigger was better.
I've known a few people who had HK pistols, my impression of their customer service is based on their experiences. They don't care.
3rdly, for those keeping track, please pick up a Glock and an HK again. I don't like the feel of the polymer that HK uses; it just feels thin in the wrong places. The HK felt clunky when I shot it; not like a Ruger, but still clunky. The controls on a USP feel like they came out of a '91 Toyota Tercel; they feel like crummy plastic.
As for the magazines, it could be argued that the polymer mags have an advantage over the metal ones in that they're pretty much impossible to dent. I've seen the polymer mags that some of the USPs come with, and they felt like the bad aftermarket mags for Glocks you used to see ten years ago; they are whippy, thin, crummy things. Like something that would come with an Airsoft. Current Glock mags are pretty Tonka-tough; I never have problems with mine. I guess the metal HK mags I saw were fine, except that for the price you could buy two or three Glock mags, and for that price they just weren't in any way better.
Want a holster? If you carry a Glock, everyone who makes holsters makes one or more for the Glock, in every conceivable configuration. There are lots of them, so prices are good. Same with other accessories.
I like to carry the Glock 19 or 23. These pistols are at a pretty ideal shootability / capacity / concealability ratio, even for a smaller guy like me. The USP compact is probably fine... It's nice being able to use Glock 22 mags as a reload for my Glock 23, and Glock 17 or 18 mags for my Glock 19... As for the 'slipperiness' issue... don't know what you're talking about. Never had a problem holding onto mine.
5th(ish)... How is HK a 'better' gun again? Why are the dovetails so deep in their frame, by the way? I've seen HK slides that cracked at the rear dovetail cut; wtf is that about? Is that due to those awesome metal sights? Why is it that metal sights are better, by the way, because I've been hitting fine with my substandard plastic ones. I've got one set of meprolight (metal) sights on one pistol and the plastic adjustable sights on the other... the adjustment feature has come in handy, is easy to use, and is no bigger than most combat sights. Pretty good for junky plastic sights, I guess. Especially on a pistol that cost me $430 out the door, brand new. The Meprolight sights were installed for me by Glock a few years ago for $55, shipped (those were the days...) Glock pistols have fewer moving parts and are just simpler machines. Mine always work.
I've had one problem with my Glocks; the first one I bought used to stovepipe when it was new. I sent it to them, they lightly polished the feed ramp, and it never did it again. Since then, smooth sailing. There are going to be more stories about Glocks; there are just more Glocks out there than anything else.
And at the risk of being labelled a 'follower', I like Glocks. This isn't merely due to the fact that I think HKs are too spendy; I just didn't like them, price be damned. There are a lot of shooters who've jumped ship on Glock because 'everyone has a Glock', or because someone told them the triggers were no good. Yeah, they're different, but it's not insurmountable. It shouldn't be anything that 200 rounds and a buddy looking over your shoulder can't cure. You can buy a lot of extra practice ammo for $300.
I like the simplicity, the straightforward manual of arms, the subtle streamlined aesthetic, and the practicality of Glock. You didn't specify, but I assume that you prefer the perceived 'shootability' and the tech appeal of HK. I like a nice light single action trigger too, but not when it comes with a ridiculous double action trigger; the HK trigger didn't do it for me. For that set-up, I prefer Sig. I've seen the LEM trigger... isn't that pretty much their equivalent of a Glock safe-action trigger? I mean, it's double action, only lighter? Like, pre-cocked lighter, right?
So, that's why I like the Glock better, just my experiences and impressions, not trying to bag on you. Although I think HKs probably comes with a little elitist-factor on them. And yeah, they look cool. Glocks are a little bit boring for some; boringly reliable, and with a subtle, plain shape. Still, if I could only keep one pistol, it'd be one of my Glocks.